Accommodation, or the adjustment made by the eye for seeing at different distances, is often characterized by convergence and ocular muscle fatigue when a patient attempts to focus a sharp image--particularly one near to the eye--on the eye's retina for more than a minimal period of time. Such ocular fatigue typically may be uncomfortable for the patient, making examinations and procedures performed during the period less pleasant for the patient and, consequently, for the practitioner as well. Existence of accommodation and convergence also may corrupt measurements made during various ocular examinations, potentially rendering eyeglass lens prescriptions inaccurate. Because a patient may tend to reposition a subject eye (or allow it to wander) as the ocular muscles tire, accommodation also may affect ophthalmic and medical procedures, including modern laser surgeries and retinal photography, which require that the subject eye remain stationary for relatively long periods.
A variety of means to counteract accommodation of the eye have thus been developed or suggested. Paralytic drugs, for example, may be used to immobilize the muscles controlling the lens of an eye and render it motionless when necessary or desired. The technique of "fogging," or placing a predetermined sequence of lenses before a subject eye, additionally may be used to relax accommodation of the eye when using auto-refractometers or similar instruments to determine the appropriate corrective lenses for a particular patient. Cornsweet U.S. Pat. No. 3,843,240, incorporated herein in its entirety by this reference, discloses an alternative method for relaxing accommodation of an eye. As described in the Cornsweet patent, relaxation of accommodation may be produced by presenting a defocused flashing light source to an eye through a pin-hole aperture positioned a selected distance from the eye's lens. Trachtman U.S. Pat. Nos. 4,533,221 and 4,660,945, also incorporated herein in their entireties by this reference, discuss other techniques for performing accommodation training.
Among the equipment frequently used by practitioners for eye examinations is the optical slit lamp. Commercially available slit lamps usually include a Galilean binocular microscope connected to optional accessories such as photographic systems (if, e.g., retinal photography is to be performed or recorded measurements are desired), Pachometers (for measuring corneal thickness), or Goldmann applanation tonometers (for assessing eyeball tension). Such slit lamps also may be integrated with laser transmission or other systems for performing ophthalmic surgery or used by neurologists in evaluating, for example, ocular muscle paralysis or the existence of ocular tumors.
One commercial slit lamp, the Topcon Photo Slit Lamp SL-5D available from the Topcon Instrument Company of America, 65 West Century Road, Paramus, N.J. 07652, includes an annular fixation wand or target having a luminous fiber optic tip. The target is connected to the end of an extendable arm and may be positioned by the practitioner near a patient's eyes to attract the patient's attention. The patient is directed to focus both eyes--including the subject eye--on the illuminated target, thereby positioning the subject eye as necessary to perform the optical examination or procedure.
During the examination the practitioner may reposition the subject eye simply by moving the illuminated target. Repositioning the target, however, typically requires that the practitioner interrupt the examination, peer away from the binocular microscope to the extendable arm, and physically adjust the arm until the target is appropriately located. Because trial-and-error techniques must be used to reposition the target, time consuming delays often exist when frequent repositioning occurs. Moreover, accommodation and convergence result when the patient attempts to focus on the nearby target, causing ocular muscle strain and fatigue strain and their consequent examination-related problems.